1. Field of the Invention
The invention pertains to guides for roller valve lifters for internal combustion engines to prevent rotation of the valve lifter about its axis.
2. Description of the Related Art
Valve lifters for internal combustion engines reciprocate within the engine block and through a lifter rod operate the intake and exhaust valves. The lower end of roller valve lifters includes a roller which engages a lobe upon the engine camshaft. By using a roller at the lower end of the valve lifter, friction between the lifter and camshaft is reduced providing superior engine performance. However, the lifter roller must rotate about an axis parallel to the axis of rotation of the camshaft and guide means must be used to properly maintain the orientation of the valve lifter in this respect.
Orientation of roller valve lifters to the camshaft is usually accomplished by forming a flat orientation surface on the valve lifter which is oriented to the axis of the valve lifter roller and cooperates with a guide engaging the lifter orientation surface to prevent rotation of the valve lifter about its axis. Usually, two parallel flat surfaces are defined upon each lifter located upon opposite sides of the lifter axis.
In the past, valve lifter guides for internal combustion engines to prevent valve lifter rotation have been formed of metal and include flats which correspond to the configuration of the lifter flats. The lifter reciprocates within the guide openings and the relationship between the guide openings and lifter flats prevents valve lifter rotation. The metal-to-metal contact between the valve lifters require clearances and the guides produce wear which increases the clearances between the moving parts, and excessive noise may be generated and improper cam lobe tracking can occur. Further, conventional metal valve lifter guides are relatively heavy, expensive to manufacture and assemble within the engine, and are prone to improper assembly if care is not taken.
Many of the aforementioned shortcomings of internal combustion engine valve lifter guides have been overcome by the applicants' roller valve guide shown in U.S. Pat. No. 5,088,455. The lifter guide shown in this patent is preferably formed of synthetic self-lubricating material and is inexpensive to manufacture, long wearing and easy to install. However, the valve lifter guide shown in U.S. Pat. No. 5,088,455 is of such a construction as to accommodate only certain types of internal combustion engines, and cannot readily be used with some types of V-block or straight engines.